An electric power steering device is known in the art, according to which a steering operation of a vehicle driver is assisted by an electric motor. Miniaturization, weight saving and higher performance are required for the electric motor.
According to one of prior arts, for example, as disclosed in Japanese Patent Publication No. 2003-204654, more exactly as shown in FIGS. 14 and 15 thereof, an electronic control unit (also referred to as a controller) is attached to an electric motor in such a direction parallel to a rotating shaft of the electric motor, which is composed of a motor casing, a stator, a rotor, the rotating shaft and so on. The controller is composed of a heat sink, a metal board, a control board and so on. The electric motor and the controller are connected to each other in such a way that an opening portion formed in the electric motor and an opening portion formed in the controller are opposed to each other. Lead wires are arranged so as to pass through the respective opening portions of the electric motor and the controller, so that coils wound on the stator of the electric motor are electrically connected to wires formed on the metal board of the controller. In addition, other lead wires pass through the respective opening portions of the electric motor and the controller, so that a position sensor for detecting a rotational angle of the electric motor is electrically connected to wires formed on the control board of the controller.
According to another prior art, for example, as shown in FIGS. 32 and 33 attached to the present application, a controller 101 is attached to an axial end of an electric motor 100. The controller 101 is so designed that its outer diameter is equal to or smaller than that of a motor casing 102 of the electric motor 100. Multiple flanged portions 103 of the controller 101, which are outwardly extending in a radial direction, are opposed to corresponding projecting portions 104 of the motor casing 102, which are likewise outwardly extending in the radial direction, and the electric motor 100 and the controller 101 are fixed to each other by screws 105.
According to the electric motor of the above first-mentioned prior art (JP 2003-204654) a size in a radial direction becomes too large and it may be a problem that a larger mounting space is necessary when the electric motor is mounted in a vehicle.
According to the electric motor of the other prior art, as shown in FIGS. 32 and 33, when the flanged portions 103 as well as the projecting portions 104 are designed so that an outer diameter of the electric motor (including the flanged and projecting portions) is within a required range, then the outer diameter of the electric motor and the controller becomes too small and thereby a decrease of a motor output may be a problem.
In addition, according to the electric motor of the above prior art (JP 2003-204654), it may have a problem that extraneous material may come into the motor casing through the opening portion thereof and operation of the stator and/or rotor may be adversely affected.